Method of tipping-off exhaust tubing



Filed July 9, 1964 W. E. WILSON ETAL METHOD OF TIPPING-OFF EXHAUST TUBING FIG. I.

2 Sheets-Sheet l INVENTOR William E. Wilson and Harold A. Zimmerman ATTORNEY m 1967 w. E. WILSON ETAL 5 METHOD OF TIPPING-OFF EXHAUST TUBING 2 Sheets-Sheet Filed July 9, 1964 FIG. ll.

FIG. l3.

United States Patent )fiice 3,3 13,6 l 9 Fatented Apr. 1 1 1 967 3,313,610 METHOD OF TIPPING-OFF EXHAUST TUBING William E. Wilson, Cedar Grove, and Harold A. Zimmerman, Lake Hiawatha, N.J., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed July 9, 1964, Ser. No. 381,489 6 Claims. (CI. 6534) The present invention relates to a method of sealing evacuated envelopes and, more particularly, to a method for tipping-off a glass exhaust tube extending from an evacuated container such as an incandescent or discharge lamp.

In the tipping-off of relatively large exhaust tubes on fluorescent lamps, a serious shrinkage problem has heretofore existed which materially affected manufacturing costs. Due to the flare cavity size from which the exhaust tube projects, as well as the diameter of the latter, it has been necessary to direct the tipping fire down into the flare, with the flame impinging on one side of the large diameter tubing. The glass in such area accordingly melts and pulls in to form a bubble which seals the exhaust tube and thereafter two fires at right angles to the bubble melt and sever the tubing. Shrinkage occurs when the bubble forming flame, which is necessarily angulated downward, follows the bubble down the relatively large exhaust tubing causing breakage thereof.

It is accordingly an object of the present invention to provide a method of tipping-off exhaust tubes which minimizes shrinkage by decreasing the likelihood of breaking of the tube during formation of the sealing bubble.

Another object of the present invention is the provision of a method of tipping-oft relatively large exhaust tubes of fluoroescent lamps as near as possible to the flare cavity to prevent interference of the sealed exhaust tube with the lamp base and at the same time minimizing the possibility of breakage of the exhaust tube.

A further object of the present invention is the provision of a method for tipping-off a relatively large exhaust tube of a fluorescent lamp in close proximity to the flare cavity and controlling the fire pattern of the heating fires to eliminate the danger of destroying the flare seal and at the same time minimizing the likelihood of the fires undesirably thinning the bubble wall with the possibility of seal destruction.

The foregoing objects of the present invention, together with other objects which will become apparent to those skilled in the art from the following description, are achieved by providing a method of tipping-01f the exhaust tubulation of an evacuated device wherein the heating fires are so disposed relative to the tubulatoin, or the latter is so shielded, as to produce a heating gradient that causes the side of the tubulation normal to the heating fires to suck in and form a bubble which seals off the tubulation. This is then followed by moving of the tubulation further into the heating fires, or by removal of the shield from about the tubulation, to cause the increased temperature to enable severing of the latter without destruction of the bubble seal.

The present invention can be readily understood by reference to the accompanying drawings wherein:

FIGURE 1 is a fragmentary elevational view of a fluorescent lamp depending from the customary exhaust head of an evacuating machine and with the tipping-off burner in place;

FIG. 2 is a view similar to FIG. 1 but taken at right angle to the latter and with the tipping-off fires directed at the exhaust stem preparatory to sealing the latter;

FIG. 3 is a secional view taken along the line III-III of FIG. 2 and looking in the direction indicated by the arrows;

FIG. 4 is a view identical to FIG. 3 except that it shows the sealing of the exhaust tubulation by formation of a bubble after the lapse of a short time of heating of such tubulation by the tipping-01f fires;

FIG. 5 is a fragmentary elevational view similar to FIG. 1 but showing the completion of the sealing bubble by collapse of the tubulation wall as seen in FIG. 4;

FIG. 6 is a sectional view similar to FIG. 4 but showing the sealed tubulation of FIGS. 4 and 5 moved into the cutoff or severing position thereof relative to the tipping-off fires;

FIG. 7 is a fragmentary elevational view of the completed sealed and severed exhaust tubulation protruding but a short distance above the flare tube cavity following cut-off as shown in FIG. 6;

FIG. 8 is a fragmentary elevational view similar to FIG. 1 but showing a slight modification which the present invention may take;

FIG. 9 is a View identical to FIG. 8 except it is taken at ninety degrees to the latter;

FIG. 10 is a cross-sectional view taken on the line XX of FIG. 8 and looking in the direction indicated by the arrows;

FIG. 11 is a view similar to FIG. 5 in that it shows completion of the sealing bubble by collapse of the tubulation wall using the modification of the present inveniton illustrated in FIGS. 8, 9 and 10;

FIG. 12 illustrates cut-off of the tubulation by removal of the heat-shield in accordance with the modification of the present invention as first shown in FIG. 8; and

FIG. 13 is a view similar to FIG. 12 but taken ninety degrees relative to the latter and showing the exhaust tubulation completely sealed and severed .by the modification of the invention as shown in FIG. 8.

By reference now to the drawings, a fluorescent lamp 5 is shown in FIG. 1 wherein its exhaust tubulation 6 is secured to an exhaust head 7 forming part of an exhaust machine which may be of a well-known type such as that shown in US. Patent No. 2,247,513, granted July 1, 1941, to A. J. Marshaus. As shown, the exhaust tubulation 6 extends downwardly through the flare tube cavity 8 (FIGS. 5 and 7) of the envelope of the fluorescent lamp 5 for the purposes of evacuating and sealing the latter. In order to protect a seal 9 and lead wires 10 of the lamp 5 during the tipping-off operation, a conically shaped heat baffle 12 surrounds the tubulation 6 and covers the seal 9, as can be seen partciularly in FIG. 5. After the lamp 5 has been evacuated in the usual manner through the exhaust tubulation 6 and filled with a predetermined amount of mercury and an inert gas at appropriate indexed positions of the head 7, it is then ready for tipping-otf at another indexed head position. The pressure within the envelope of the lamp 5 is less than the pressure external to the envelope of the lamp 5.

For purpose of tipping-off, a pair of parallel tipping-off burners 13 forming a torch flame are spaced approxi- 3 mately one inch apart to allow the exhaust tubulation 6 to pass therebetween, with the lateral torch flame from the forming fires being directed slightly downward in the direction of the flare cavity 8 as seen particularly in FIG. 2. In the tipping-off position of the exhaust head 7 the burners 13 are indexed to position the exhaust tubulation 6 on a line approximately midway therebetween with only about one third of the periphery of such exhaust tubulation actually in the path of the fire from the burners, as shown in FIG. 3.

When so disposed, the heated periphery side of the exhaust tubulation 6 is softened and a bubble 14 (FIG. 5) forms at right angles to the torch flame direction. Immediately thereafter the burners 13 are indexed to place the entire periphery of the exhaust tubulation 6 in the full heat from the torch flame, as seen in FIG. 6, in which position the exhaust tubulation is then severed in the manner shown in FIG. 7 upon a slight longitudinal separating movement. Accordingly the thin membrane of the bubble 14 is always shielded from the torch flame of the forming fires by the section of the exhaust tubulation not softened in bubble forming, with the result that the lamp 5 is completely sealed without destruction of the thin membrane bubble which would otherwise result in the shrinkage loss of the entire lamp 5. Thus the bubble 14, after formation, cools to less than its softening temperature and is then protected from further appreciable heating by the sealing flames.

The modification of the present invention as shown in FIGS. 8 to 13, inclusive, differs from that previously above described merely in the elimination of an index step of the tipping-off burners 13 by initially positioning the exhaust tubulation entirely within the area of the torch flame but shielding it (FIGS. 10 and 11) by a movable shield (FIGS. 8 to 11) so that only the same one third of its periphery is heated, as previously described relative to FIG. 3. After heating such limited peripheral area to the softening point, with formation of the thin membrane bubble 14- (FIG. 11) at right angles to the torch flame, such shield 15 is moved as shown in FIG. 12, thus exposing the remaining periphery of the exhaust tubulation 6 to the full heat of the torch flame. Again this causes severing of such exhaust tubulation as shown in FIGS. 12 and 13 upon slight longitudinal movements, without destruction of the thin membrane bubble and with the tipped-off exhaust tubulation sufficiently within the flare cavity as to in no way interfere with the application of the customary base to the lamp end.

It should thus become apparent to those skilled in the art that a method for tipping-off evacuated envelopes such as incandescent and discharge lamps has been herein provided in which heating of the exhaust tubulation is initially restricted to a limited peripheral area to cause the formation of a thin membrane bubble at right angles to the torch flame direction thus sealing-off the envelope. Immediately thereafter the entire periphery of the exhaust tubulation is heated to a temperature sufficient to enable severing thereof by a slight longitudinal movement and without destruction of the thin membrane sealing bubble.

Although several embodiments of the present invention have been herein shown and described, it is to be particularly understood that still further modifications thereof may be made without departing from the spirit and scope of the present invention.

We claim as our invention:

1. The method of tipping-off a portion of a vitreous exhaust tubing which opens into and projects from a vitreous envelope, wherein the external pressure surrounding the tubing is greater than the pressure within said envelope, and wherein the portion of the tubing to be tipped-off is laterally surrounded by a portion of said envelope, which method comprises:

(a) placing a flame-shielding member about the portion of said tubing to be tipped-off and over the surrounding portion of said envelope;

(b) applying sealing flames laterally over said flameshielding member and onto a limited peripheral portion of that part of said exhaust tubing to be tippedoif to heat such tubing portion to its softening temperature and permit such softened tubing portion to suck in toward said envelope in the form of a thin bubble which seals said exhaust tubing and is protected from further appreciable sealing-flame heating;

(c) permitting the now-protected formed sealing bubble to cool to less than its softening temperature and heating, with said laterally disposed sealing flames, the entire periphery of that portion of said exhaust tubing which is adjacent the formed sealing bubble and positioned away from said envelope with respect to said sealing bubble; and

(cl) causing a separating movement between said envelope and that portion of said exhaust tubing which is now sealed from said envelope to cause the nowsoftened portion of said exhaust tubing to sever.

2. The method of tipping off the vitreous exhaust tubulation protruding from an evacuated envelope having a seal, which method comprises:

(a) projecting a flame upon only a limited portion of the periphery of the exhaust tubulation to cause such portion to be sucked in and form a thin membrane sealing bubble remote from said flame, and

(b) thereafter flame heating the remainder of the periphery of said exhaust tubulation adjacent said sealing bubble to sever such tubulation thereby tipping off said tubulation without destruction of said thin membrane sealing bubble.

3. The method of tipping off a vitreous exhaust tubulation protruding from an evacuated envelope having a seal,

which method comprises:

(a) heating said exhaust tubulation by positioning it partially in the path of a torch flame to plasticize a limited portion of the periphery of such exhaust tubulation to cause the plasticized portion to be sucked in and form a thin membrane sealing bubble remote from said flame path, and

(b) thereafter flame heating the remainder of the periphery of said exhaust tubulation adjacent said sealing bubble to sever such tubulation upon slight longitudinal movement thereof, thereby tipping off said tubulation without destruction of said thin membrane sealing bubble.

4. The method of tipping off a vitreous exhaust tubulation protruding from an evacuated envelope having a seal, which method comprises:

(a) heating said exhaust tubulation by positioning it partially in the path of a torch flame to plasticize a limited portion of the periphery of such exhaust tubulation to cause the plasticized portion to be sucked in and form a thin membrane sealing bubble remote from said flame path, and

(b) thereafter applying the torch flame to the remainder of the periphery of said exhaust tubulation adjacent said sealing bubble through relative movement of one of said torch flame and said tubulation to sever the tubulation thereby tipping off said tubulation without destruction of said thin membrane sealing bubble.

5. The method of tipping off a vitreous exhaust t-ubulation protruding from an evacuated envelope having a seal, which method comprises:

(a) projecting a flame upon a limited portion of the periphery of the exhaust tubulation while shielding the remainder thereof from said flame to plasticize only such limited portion and cause it to be sucked in to form a thin membrane sealing bubble remote from said flame, and

(b) thereafter directing said flame upon the remainder of the periphery of said exhaust tubulation adjacent said sealing bubble to sever such tubulation to thereby tip off said tubulation Without destruction of said thin membrane sealing bubble.

6. The method of tipping off a vitreous exhaust tubulation protruding from an evacuated envelope having a seal, which method comprises:

(a) positioning said tabulation between a pair of opposed burners,

(b) shielding a substantial portion of said exhaust tabulation,

(c) projecting a flame from said burners upon a portion of the periphery of said exhaust tubulation to plasticize such portion and cause it to be sucked in to form a thin membrane sealing bubble remote from said flame, and

(d) thereafter removing the shield completely from the path of the torch flame so that such flame heats the remainder of the periphery of said exhaust tubulation adjacent said sealing bubble to sever such tabulation thereby tipping oil said tubulation Without destruction of said thin membrane sealing bubble.

References Cited by the Examiner UNITED STATES PATENTS 7/1951 Bechard 65-34 10/1960 Madigan 6534 

1. THE METHOD OF TIPPING-OFF A PORTION OF A VITREOUS EXHAUST TUBING WHICH OPENS INTO AND PROJECTS FROM A VITREOUS ENVELOPE, WHEREIN THE EXTERNAL PRESSURE SURROUNDING THE TUBING IS GREATER THAN THE PRESSURE WITHIN SAID ENVELOPE, AND WHEREIN THE PORTION OF THE TUBING TO BE TIPPED-OFF IS LATERALLY SURROUNDED BY A PORTION OF SAID ENVELOPE, WHICH METHOD COMPRISES: (A) PLACING A FLAME-SHIELDING MEMBER ABOUT THE PORTION OF SAID TUBING TO BE TIPPED-OFF AND OVER THE SURROUNDING PORTION OF SAID ENVELOPE; (B) APPLYING SEALING FLAMES LATERALLY OVER SAID FLAMESHIELDING MEMBER AND ONTO A LIMITED PERIPHERAL PORTION OF THAT PART OF SAID EXHAUST TUBING TO BE TIPPEDOFF TO HEAT SUCH TUBING PORTION TO ITS SOFTENING TEMPERATURE AND PERMIT SUCH SOFTENED TUBING PORTION TO SUCK IN TOWARD SAID ENVELOPE IN THE FORM OF A THIN BUBBLE WHICH SEALS SAID EXHAUSE TUBING AND IS PROTECTED FROM FURTHER APPRECIABLE SEALING-FLAME HEATING; (C) PERMITTING THE NOW-PROTECTED FORMED SEALING BUBBLE TO COOL TO LESS THAN ITS SOFTENING TEMPERATURE AND HEATING, WITH SAID LATERALLY DISPOSED SEALING FLAMES, THE ENTIRE PERIPHERY OF THAT PORTION OF SAID EXHAUST TUBING WHICH IS ADJACENT THE FORMED SEALING BUBBLE AND POSITIONED AWAY FROM SAID ENVELOPE WITH RESPECT TO SAID SEALING BUBBLE; AND (D) CAUSING A SEPARATING MOVEMENT BETWEEN SAID ENVELOPE AND THAT PORTION OF SAID EXHAUST TUBING WHICH IS NOW SEALED FROM SAID ENVELOPE TO CAUSE THE NOWSOFTENED PORTION OF SAID EXHAUST TUBING TO SEVER. 